RE: [PATCH v5 0/5] ACPI 2.0: Stop defer-executing module level code

["Zheng, Lv" <lv.zheng@intel.com>]

Hi, Rafael

> From: Rafael J. Wysocki [mailto:rjw@rjwysocki.net]
> Subject: Re: [PATCH v5 0/5] ACPI 2.0: Stop defer-executing module level code
> 
> On Friday, September 23, 2016 11:26:26 AM Lv Zheng wrote:
> > After fixing ACPICA internal locking issues, we can enable the correct
> > grammar support for the table loading. The new grammar treats the entire
> > table as TermList rather than ObjectList, thus the module level code should
> > be executed right in place.
> >
> > MLC (module level code) is an ACPICA terminology describing the AML code
> > out of any control method, currently only Type1Opcode (If/Else/While)
> > wrapped MLC code blocks are executed by the AML interpreter after the table
> > loading. But the issue which is fixed by this patchset is:
> >    Not only Type1Opcode, but also Type2Opcode will be executed as MLC and
> >    MLC is not defer-executed after loading the table, but is executed right
> >    in place.
> >
> > The following AML code is assembled into a static loading SSDT, and used
> > as an instrumentation to pry into the de-facto standard AML interpreter
> > behaviors:
> >   Name (ECOK, Zero)
> >   Scope (\)
> >   {
> >       DBUG ("TermList 1")
> >       If (LEqual (ECOK, Zero))
> >       {
> >           DBUG ("TermList 2")
> >           Device (MDEV)
> >           {
> >               DEBUG (TermList 3")
> >               If (CondRefOf (MDEV))
> >               {
> >                   DBUG ("MDEV exists")
> >               }
> >               If (CondRefOf (MDEV._STA))
> >               {
> >                   DBUG ("MDEV._STA exists")
> >               }
> >               If (CondRefOf (\_SB.PCI0.EC))
> >               {
> >                   DBUG ("\\_SB.PCI0.EC exists")
> >               }
> >               Name (_HID, EisaId ("PNP9999"))
> >               Method (_STA, 0, Serialized)
> >               {
> >                   DEBUG ("\\_SB.MDEV._STA")
> >                   Return (0x0F)
> >               }
> >           }
> >           DBUG ("TermList 4")
> >       }
> >       Method (_INI, 0, Serialized)
> >       {
> >           DBUG ("\\_SB._INI")
> >       }
> >   }
> >   Scope (_SB.PCI0)
> >   {
> >       Device (EC)
> >       {
> >           ...
> >       }
> >   }
> > The DBUG function is a function to write the debugging messages into a
> > SystemIo debug port.
> > Running Windows with the BIOS providing this SSDT via RSDT, the following
> > messages are obtained from the debug port:
> >   TermList 1
> >   TermList 2
> >   TermList 3
> >   \_SB.MDEV exists
> >   TermList 4
> >   \_SB._INI
> >   ...
> >
> > This test reveals the de-facto grammar for the AMLCode to us:
> > 1. During the table loading, MLC will be executed by the interpreter, this
> >    is partially supported by the current ACPICA;
> > 2. For SystemIo, not only after the _REG(1, 1) is evaluated (current ACPICA
> >    interpreter limitation), but when the table is being loaded, the
> >    SystemIo (the debugging port) is accessible, this is recently fixed in
> >    the upstream, now all early operation regions are accessible during the
> >    table loading;
> > 3. Not only Type1Opcode, but also Type2Opcode will be executed as MLC and
> >    MLC is not executed after loading the table, but is executed right in
> >    place, the Linux upstream is not compliant to this behavior.
> >
> > The last compliance issue has already been clarified in ACPI 2.0
> > specification, so the compliance issue is not that Linux is not compliant
> > to the de-facto standard OS, but that Linux is not compliant to ACPI 2.0.
> > Definition block tables in fact is defined by the spec as TermList, which
> > has no difference than the control methods, thus the interpretion of the
> > table should be no difference that the control method evaluation:
> >      AMLCode := DefBlockHeader TermList
> >      DefMethod := MethodOp PkgLength NameString MethodFlags TermList
> > Now the new upcoming ACPI specification has been clarified around the above
> > grammar primitives, so we need to implement them for Linux.
> >
> > This patchset also contains 2 required fixes generated to fix the
> > regressions detected by the ACPICA ASLTS tool. The ASLTS 'table' test suite
> > has detected such regressions. The fixes have been accepted by the ACPICA
> > upstream (please refer to the ACPICA upstream URL in the description of the
> > 2 patches). And they are sent to Linux community as urgent materials along
> > with the module level code enabling series. With the additional regression
> > fixes, new grammar changes have passed all ASLTS 'table' cases:
> >   https://bugs.acpica.org/show_bug.cgi?id=1327
> >   https://github.com/acpica/acpica/pull/177
> >
> > Lv Zheng (5):
> >   ACPICA: Tables: Fix "UNLOAD" code path lock issues
> >   ACPICA: Parser: Fix a regression in LoadTable support
> >   ACPI 2.0 / AML: Enable correct ACPI subsystem initialization order
> >     for new table loading mode
> >   ACPI 2.0 / AML: Improve module level execution by moving the
> >     If/Else/While execution to per-table basis
> >   ACPI 2.0 / AML: Fix module level execution by correctly parsing table
> >     as TermList
> 
> [1-2/5] queued up for 4.9.
> 
> The rest I'd prefer to keep in linux-next for some time before they go in,
> so let's make them 4.10 material if not urgent for some reasons.

I see.
We could have [4-5/5] enabling patch pending for a period in order for more validations.
But should we have 3/5 queued up?
It's prepared for the 3rd mode of MLC support.
So it is a no-op for the current Linux kernel.
But having it upstreamed is useful to complete the mode (but not enable it).

I've been asked for why ECDT is implemented in the current way.
If PATCH 3/5 in the upstream, the reviewer should soon realize what the purpose of the ECDT change is.

Thanks and best regards
Lv